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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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    <script>
        // 二维数组 数组里面套数组
        var arr =[[1,2],[3,4]];
        console.log(arr[0][1]);  // 2
        console.log(arr[1][0]);  // 3
    </script>
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